The present invention relates to methods and apparatus for starting single shaft gas turbine driven or electric motor driven compressor sets, and in a further embodiment relates to methods and apparatus for starting large single shaft gas turbine driven compressor sets of greater than 43,700 horsepower.
Present compressor plants, such as those used in liquified natural gas (LNG) plants, use either the smaller two-shaft gas turbine driver (which has no driver compressor starting problems) or the larger, more cost-effective single-shaft gas turbine driver with its presently-associated complex compressor starting method and apparatus. While two-shaft gas turbine drivers are suitable for starting compressors, they are commercially unavailable in sizes greater than 43,700 horsepower. There is a need for a device which can efficiently start single-shaft gas turbine driven centrifugal compressor sets in processes requiring total power up to 350,000 horsepower and more.
Large single-shaft gas turbines have a standard starting system that at most can only start up the gas turbine driver itself and an unloaded, connected electric generator. A specific problem with the single-shaft gas turbine is that everything is connected mechanically on a single common shaft, hence the starting device must start up not only the gas turbine itself, but also the connected load (for example, an electric generator or centrifugal compressor). Everything must be started up and accelerated simultaneously from rest continuously up to full speed. The added load produced by an electric generator in an unloaded state, that is, not connected to the electrical power grid during starting, can be handled by a single-shaft gas turbine""s standard starting system, but not the inertia and aerodynamic loads associated with a large centrifugal compressor.
For starting up large, single-shaft gas turbine compressor sets, an additional starting device (an electric motor or steam turbine helper driver or engine) is typically added at the outboard free end of the driven compressor(s). This starting device can either be a steam turbine driver or an electric motor driver, which typically includes a Variable Frequency Electrical Drive system (VFD) to provide variable speed. The electric motor driver requires an external source of electric current, while the steam turbine requires an external source of steam, hence both starting device types are not independent or stand-alone devices. Because both of these systems, in turn, have many sub-systems, they are costly, complex, and are very maintenance intensive.
Further, many times because of a remote location, a plant does not have a readily available nearby electrical grid or a steam system. Steam systems require a large source of water. In addition, it is generally more economical to utilize air instead of water for cooling.
It is desirable to provide a method and apparatus to start up large loads, such as centrifugal compressors, axial compressors and the like, which is simpler, lower in cost, and requires less maintenance than the systems currently available.
Accordingly, it is an object of the present invention to provide a less costly, less complex, less maintenance-intensive, more reliable and more efficient device and method utilizing proven equipment for starting up compressors and specifically single-shaft, gas turbine-driven or electric motor-driven compressor sets.
An additional object of the invention is to provide a device and method that can be used to start up centrifugal compressors, axial compressors, and combinations thereof
Another object of the present invention is to allow the more cost-effective single-shaft gas turbine to be used more readily for gas turbine compressor drivers.
In carrying out these and other objects of the invention, there is provided, in one form, a power transmission system for driving at least one compressor. The system has a driver, where one end of the shaft is the driver output shaft. A compressor starting torque converter (CSTC) is also present which has a pump impeller on an input shaft and a turbine wheel on an output shaft, where the CSTC input shaft is coaxially connected to the driver output shaft. Further, there is a compressor with an input shaft coaxially connected to the CSTC output shaft. The CSTC further comprises a lock-up device between the pump impeller and the turbine wheel to lock the impeller and the turbine wheel together. The driver may be a single shaft gas turbine or an electric motor. The compressor may be a centrifugal compressor, an axial compressor or a combination thereof.